This invention relates generally to spark gaps for use as voltage limiters or surge suppressors and particularly to power spark gaps for conduction of thousands of amperes of current in response to high voltages such as 100 kilovolts or more.
Power gaps of the general type to which the present invention relates have been previously used, for example, to protect series capacitors from overvoltages due to faults or lightning surges on transmission lines. In such applications, it is highly desirable to have a compact and economical device that is capable of consistent performance upon repeated operation over a long period of time. One form of device presently used has a relatively large, well ventilated, metal cabinet enclosing spherical gap electrodes. These are generally bulky and expensive and also may deteriorate in performance upon repeated firings.
Another form of device that has been used is that including a relatively small porcelain housing enclosing a spark gap of carbon electrodes in an arrangement that provides a toroidal to a planar gap interface. Such a device is that described in Riggins U.S. Pat. No. 4,277,719, July 7, 1981 which is herein incorporated by reference for its general description of such devices. Such a device operates quite well in terms of consistency of sparkover level and achieves such performance in a relatively compact economical assembly. One respect in which it is desirable to improve the performance of such devices is the consistency of the sparkover level upon different polarities of voltage as it is the case that the gap must fire regardless of the polarity of the AC voltage on its electrodes. Spark gaps of the type described in the above-mentioned patent may exhibit a variation in sparkover level for opposite polarities of up to about 18 percent. Also, such devices exhibit less change of sparkover level for a change in electrode spacing than is sometimes desirable.
In accordance with the present invention a new design of power spark gap device is provided that incorporates electrodes of a hollow, hemispherical configuration inside a porcelain enclosure. This enables a considerably higher sparkover-to-spacing ratio and an improved impulse polarity response than prior designs. Incorporated into the electrodes is a unique arcing tip support that provides a short low resistance path, via vent holes through the carbon electrode bodies, for the arc plasma to communicate with higher conductive sleeves within the electrode bodies. This prevents the arc from migrating to undesired areas such as the copper support of the electrodes. The vents through the electrode bodies also provide pressure relief for the expanding arc gases via the hollow support tube supporting one of the electrodes. This design provides a sparkover versus spacing curve that is almost identical to laboratory sphere gaps of comparable size and permits an increase of approximately 150% in the voltage rating of an equivalent existing design with close similarity of positive and negative polarities.
The above mentioned and other aspects of the invention will be better understood with reference to the following description and accompanying drawing.